Currently, high-density and high-quality transmission devices are desired due to the spread of communication using the Internet. Thus, a transmission device is desired to have a function that supports a plurality of services such as Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) and the Ethernet (registered trademark).
In addition, in a transmission device such as an L2 switch, an operation clock of a shared buffer processing unit is determined based on an assumption that packet signals input from a plurality of input ports are input at the full rate. In addition, in the transmission device, reduction of power consumption is desired.
However, in the above-described transmission device, an operation clock rate may be excessive when the input rate is low, because the operation clock is determined by assuming the input at the full rate. As a result, power consumption may increase owing to the excessive operation clock rate.
In addition, in the transmission device that supports the plurality of services such as SONET/SDH, an input port that is used for another service is not used out of the plurality of input ports. However, the operation clock is determined by assuming that all input ports are used. Therefore, even if there is an unused input port in the transmission device, a read enable signal is output to the unused input port in addition to the used ports and electric power is undesirably consumed.
Japanese Laid-open Patent Publication Nos. 2007-74607, 2001-144753, and 2011-61443 are examples of the related art.